Electronic organ key



March 17, 1964 R MCKEE ETAL 3,125,737

ELECTRONIC ORGAN KEY Filed Dec. 16, 1959 &1

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Rama/ 42d 7/ZCJTQE W165 771 Ez'c United States Patent p 3,125,737 ELECTRUNEIC ORGAN KEY Richard W. McKee, Lake Forest, and Charles M. Rich,

Chicago, IlL, assign'ors to Welding tiervice, line, Frantilin Parir, Ill., a corporation of California Fiied Dec. 16, 1959, Ser. No. 860,022 3 (Jlairns. (Ci. Kid-p9) The present invention relates to a contact assembly for an electronic organ and more particularly to an improved graded resistance type contact assembly for an electronic organ.

For an electronic organ to sound like a pipe organ, the ability to release each note of music with a gradual buildup and decay should be a built-in or inherent feature of the electronic organ. At the same time, the build-up and decay should be controllable in degree so that the touch and expression of each individual artist becomes part of the music played. In other words, each key of an electronic organ should be capable of completely controlling the rate of build-up and decay of the note.

In the key construction most widely used, movement of the key closes and opens a number of contacts. The contacts, when closed, instantly release the electronic frequency of the note to an amplifying system, and whatever volume is set on the electronic organ is instantaneously present. Accordingly, the key releases a note too mechanically and therefore, leaves little or no room for the attainment of musical expression.

Previously available graded resistance type contact assemblies have been and have required precise workmanship and adjustment in order to operate satisfactorily. Moreover, the contact assemblies have had a tendency to be noisy.

An object of the present invention is the provision of an improved graded resistance type contact assembly for an electronic organ. Another object of the invention is the provision of a contact assembly for an electronic organ which provides a controllable rate of attack and decay of a note of music. A further object is the provision of a graded resistance type contact assembly for an electronic organ which is durable in use and inexpensive to manufacture.

Other objects and advantages of the present invention will become apparent by reference to the following description and the accompanying drawings.

In the drawings:

FIGURE 1 is a fragmentary vertical cross-section of a contact assembly of an electronic organ showing various features of the present invention;

FIGURE 2 is a schematic perspective view of the contact assembly shown in FIGURE 1; and

FIGURE 3 is a fragmentary enlarged cross-sectional View showing another embodiment of the present invention.

Generally, a contact assembly in accordance with the present invention is designed to provide a controllable resistance between contact members. The illustrated contact assembly comprises a pair of contacts, each of which contacts is connected to an electronic circuit. Means are provided for moving the contacts relative to each other so that they contact each other at an area of contact. The contacts are coated with a material having a high resistivity so that as the area of contact is increased the resistance between the contacts is decreased.

More specifically, the contact assembly illustrated in FIGURES 1 and 2 includes an elongated generally horizontally extending contact member or bus bar 10 which is supported at both ends by suitable insulators 12. The insulators 12, in turn, are supported by a suitable frame 14 disposed in an electronic organ. One end of the bus 3,125,737 Patented Mar. 17, 1964 bar It) is connected by a conductor 16 to a suitable output circuit 117 of the electronic organ.

In the embodiment illustrated in FIGURES 1 and 2, the bus bar It is composed of an elongated cylindrical wire 18 of conductive material such as copper. The wire 18 is covered with a coating 19 of a material having a high resistivity as hereinafter described.

Disposed at right angles to the bus bar 10 is a flexible, generally cylindrical, elongated contact member 20. As illustrated, the contact member 20 is supported in a horizontally extending position and in spaced relation to the bus bar It by a suitable insulator 22 connected at one end of the contact member 20. The insulator 22 in turn, is mounted on the frame 14. The fixed end of the contact member 2% is connected by a conductor 24 to a suitable tone source 25 of the electronic organ.

As illustrated, the free end of the contact member 20 extends through an aperture 26 in an actuator 23 of insulating material. The actuator 28, which is employed to move the contact member 20 toward the bus bar Id, is moved downwardly by pressing a key (not shown) on the keyboard of the electronic organ.

As shown in FIGURE 1, the contact member 20 touches the bus bar It at an area of contact 39. The movement of the actuator 28 is made such that the contact member 269 wraps partially around the bus bar 10. Accordingly, the area of contact 3i) is initially small but, as the contact member 2% is wrapped farther about the bus bar to, the area of contact 36 increases.

The contact member 2% is composed of material having a high elasticity so that when the actuator 28 is returned to its normal position by a spring (not shown) or such, the contact member Zii recovers to its generally horizontally extending position. In the illustrated embodiment, the contact member 2 9 includes an elongated flexible wire 32 of conductive material such as spring steel. The Wire $2 is covered with a flexible coating 34 of a material having a high resistivity as hereinafter described.

Ordinarily, in an electronic organ contact assembly a plurality of bus bars in and a plurality of contacts iii are associated with each bus bar. For purposes of explanation only, one bus bar and one of its contacts are described, but it should be understood that the other bus bars and contacts may be similarly constructed.

The material employed for the coatings I9 and 35 i is of a resistivity such that, when the contact member 20 and the bus bar It initially meet and the contact area is thus small, the resistance therebetween is high. As the contact area is increased, because of the wrapping of the contact member 2t? partially around the bus bar lit, the resistance therebetween is greatly decreased.

A material suitable for use as a coating for the contact member 21) and the bus bar it may be fabricated by dispersing particles of a material having appropriate conductivity over the wire portion of the contact member 26 and bus bar iii in such concentration as to produce the desired resistivity. Higher concentrations of particles will decrease the resistivity and lower concentrations will, of course, increase the resistivity. The particles may be supported in any suitable manner.

Conductive particles may be dispersed in a relatively non-conductive plastic which may be fabricated into the desired coating. In the plastic, conductive particles, such as carbon, in the form of graphite or carbon black, metal particles, etc, may be used.

In one illustrative embodiment, a conductive plastic is made by mixing one part by weight of aqueous emulsion containing 50 percent by weight of urea formaldehyde resin, a suitable emulsion being the one sold under the trade name of Formbond No. 436 by Industrial Adhesive Company, and one part by Weight of an aqueous emulsion containing 50 percent by weight of polyvinyl acetate, such as that sold under the trade name of Elvacet by Du Pont. Approximately 20 percent by weight of flaked graphite of a size which will pass through a 300 mesh screen is then added and thoroughly dispersed in the plastic emulsion. The resulting mixture is then diluted with sufiicient Water to provide the desired consistency. The mixture is then dispersed on the surfaces of a spring steel wire of .012 inch in diameter and a copper wire having a diameter of one-eighth inch to provide respectively the contact member and the bus bar. The plastic carrier for the graphite is then cured. Suitable conditions for curing the plastic Which has been described involve the use of a temperature of about 60 degrees C. for two hours, or drying it overnight at room temperature. The finished coating for the contact member and bus bar is about .002 inch in thickness and the resistivity is about 50 kilohms per square inch.

As another illustrative embodiment of a conductive plastic coating which may be used, one part by weight of cellulose nitrate is mixed with two parts by weight of acetone. To this mixture about one percent by weight of acetate tributyl citrate is added as a plasticizer. Approximately 20 percent by weight of flaked graphite of a size which will pass through a 300 mesh screen is then added to the mixture and thoroughly dispersed therein. The graphite plastic mixture is thinned, if necessary, with a suitable solvent, such as acetone, to produce the desired consistency and is then applied in a similar manner as that described previously to a spring wire and a copper bus. The solvent is evaporated either by air drying or by the use of suitable drying equipment. The finished coating is about .001 inch in thickness and the resistivity is about 100 kilohms per square inch.

Depending upon the resistivity desired the amount of graphite, carbon black, or other material employed as the conductor may be varied over wide limits, the amount being limited only by the resistivity desired and the mechanics of forming it into a coating of the desired thickness. Similarly, the thickness of the coating may be varied over wide limits, depending upon the resistivity of the material. Other plastic carriers also may be used including Water emulsions of plastics, solutions of plastics or hot melt plastics, the only limitations upon the plastic being that it have a high resistance, i.e., that it is substantially an insulating material, and that it may be formed into the desired layer.

It should be understood that for a given resistivity of the coating, the contact resistance when the contacts initially meet may be increased by increasing the thickness of the coating. Moreover, for a given resistivity of the coating, the contact resistance when the key is full depressed, may be decreased by increasing, the area of contact. This may be accomplished by increasing the circumference of the bus bar which comes in contact with the contact member 20. For best results, the initial contact resistance should be as high as practical, and the area of contact when the key is fully depressed should be as large as practical.

FIGURE 3 shows another embodiment of the contact assembly for accomplishing the improved results of the present invention. With the exception of the crosssectional shape of the bus bar, the parts in this embodiment are similar to those described above in connection with FIGURES 1 and 2. Similar parts to those shown in FIGURES 1 and 2 are designated with the same reference numeral.

A bus bar 40, constructed as illustrated in FIGURE 3, includes an elongated bar 42 of an insulating material, such as wood, plastic, etc. The bar 42 is generally rectangular in cross section with the surface 43 adjacent the contact member 30, being curved to correspond approximately to the maximum bend which may be tolerated in the contact member without undue stress. The curved surface 43 of the bar 42 is longitudinally grooved to provide a plurality of teeth 44.

A coating 46 of a material having a high resistivity, such as that previously described in connection with FIG- URES 1 and 2 is applied to the toothed surface 43. A wire 48 of conductive material, such as copper, is connected to the coating 46 along the longitudinal edge of the toothed surface 43 which is nearer the movable end of the contact member 20. The wire 48 is employed to connect the resistive coating 46 to the conductor 16 which in turn, is connected to the electronic circuit 17.

In operation, when the contact member 20 is moved downwardly by the actuator 28, it contacts one of the teeth 44 on the bus bar 40 spaced from the Wire 48. Consequently, the resistance of the coating 46 between the area of contact and the wire 48 is high. As the contact member 20 engages more of the teeth 44, the length of coating 46 between the contact member 20 and the wire 48 decreases. Hence, the resistance between the contact member 20 and the wire 48 decreases.

It should be understood, that for a given resistivity of the coating 46, the initial contact resistance may be increased by decreasing the thickness of the coating, or by increasing the length of the coating between the initial point of contact and the wire 48. This may be accomplished by increasing the number of teeth, or by increasing the tooth depth.

From the above it can be seen that a contact assembly in accordance with the present invention provides a controllable rate of attack and decay of a note of music. Moreover, conductive plastic employed on one or both of the contacts reduces the cost of the contacts since a precious metal coating is not required.

Various changes may be made in the above described contact assembly without departing from the spirit or scope of this invention. Various features of the invention are set forth in the accompanying claims.

We claim: a a

1. A contact assembly for an electronic organ comprising a flexible, elongated, generally cylindrical first contact member one end of which is connected to an electronic circuit, means for selectively moving said contact member, a second electronic circuit, and a second contact member connected to said second electronic circuit and supported in the path of movement of and at right angles to said first contact member so that said first contact member is selectively pressed against and partially wrapped around said second contact member at an area of contact, each of said contact members including a wire of conductive material, and a coating of synthetic, organic, non-elastomeric, conductive plastic disposed on said wire, whereby a controllable resistance is provided between said contact members which is controlled by the first contact member being pressed against and partially wrapped around said second contact member.

2. A contact assembly for an electronic organ comprising an elongated first contact member one end of which is connected to an electronic circuit, means for selectively moving said first contact member, a second electronic circuit, and a second contact member connected to said second electronic circuit and supported in the path of movement of and at right angles to said first contact member so that said first contact member is selectively pressed against said second contact member at an area of contact, said second contact member including a layer of insulating material having a serrated curved surface against which said first contact member is pressed a continuous coating of conductive plastic having a high resistivity disposed on the teeth of said serrated surface, and a wire of conductive material connected to said coating at a point spaced from the area of the coating initially contacted by said first contact member, said first contact member including a conductive wire of spring material, and a coating of conductive plastic having a high resistivity disposed on said wire.

3. A contact assembly for an electronic organ compris ing an elongated, flexible first contact member having an arcuate surface, one end of said contact being fixedly supported and connected to an electronic circuit, means for selectively moving the other end of said contact member, a second electronic circuit, and a second contact member having an arcuate surface, said second contact member being connected to said second electronic circuit and supported in the path of movement of and at right angles to said first contact member so that the arcuate surface of said first contact member is selectively pressed against the arcuate surface of said second contact member at an area of contact and wrapped partially around said second contact member, each of said contact members including a wire of conductive material and a coating of conductive plastic disposed on said wire, said conductive plastic including graphite particles dispersed in a relative nonconductive synthetic, organic, non-elastomeric plastic whereby a controllable resistance is provided between said contact members which is decreased by wrapping said first contact member around said second contact member thereby increasing the area of contact therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 1,097,053 Severy et a1. May 19, 1914 2,134,323 Beach Oct. 25, 1938 2,141,231 Trantivein Dec. 27, 1938 2,215,124 Kock et a1. Sept. 17, 1940 2,427,700 Atkinson et a1. Sept. 23, 1947 2,510,608 Stephens June 6, 1950 2,694,128 Maurin Nov. 9, 1954 2,703,356 Buchanan et a1. Mar. 1, 1955 2,931,877 Henley Apr. 5, 1960 

1. A CONTACT ASSEMBLY FOR AN ELECTRONIC ORGAN COMPRISING A FLEXIBLE, ELONGATED, GENERALLY CYLINDRICAL FIRST CONTACT MEMBER ONE END OF WHICH IS CONNECTED TO AN ELECTRONIC CIRCUIT, MEANS FOR SELECTIVELY MOVING SAID CONTACT MEMBER, A SECOND ELECTRONIC CIRCUIT, AND A SECOND CONTACT MEMBER CONNECTED TO SAID SECOND ELECTRONIC CIRCUIT AND SUPPORTED IN THE PATH OF MOVEMENT OF AND AT RIGHT ANGLES TO SAID FIRST CONTACT MEMBER SO THAT SAID FIRST CONTACT MEMBER IS SELECTIVELY PRESSED AGAINST AND PARTIALLY WRAPPED AROUND SAID SECOND CONTACT MEMBER AT AN AREA OF CONTACT, EACH OF SAID CONTACT MEMBERS INCLUDING A WIRE OF CONDUCTIVE MATERIAL, AND A COATING OF SYNTHETIC, ORGANIC, NON-ELASTOMERIC, CONDUCTIVE PLASTIC DISPOSED ON SAID WIRE, WHEREBY A CONTROLLABLE RESISTANCE IS PROVIDED BETWEEN SAID CONTACT MEMBERS WHICH IS CONTROLLED BY THE FIRST CONTACT MEMBER BEING PRESSED AGAINST AND PARTIALLY WRAPPED AROUND SAID SECOND CONTACT MEMBER. 